Over the last few decades, the electronics industry has undergone a revolution by the use of semiconductor technology to fabricate small, highly integrated electronic devices. The most common semiconductor technology presently used is silicon-based. A large variety of semiconductor devices have been manufactured having various applicability and numerous disciplines. One such silicon-based semiconductor device is a metal-oxide-semiconductor (MOS) transistor.
The principal elements of a typical MOS semiconductor device are illustrated in FIG. 1. The device generally includes a gate electrode 101, which acts as a conductor, to which an input signal is typically applied via a gate terminal (not shown). Heavily doped source 103 and drain 105 regions are formed in a semiconductor substrate 107 and are respectively connected to source and drain terminals (not shown). A channel region 109 is formed in the semiconductor substrate 107 beneath the gate electrode 101 and separates the source 103 and drain 105 regions. The channel is typically lightly doped with a dopant type opposite to that of the source 103 and drain 105 regions. The gate electrode 101 is physically separated from the semiconductor substrate 107 by a gate insulating layer 111, typically an oxide layer such as SiO.sub.2. The insulating layer 111 is provided to prevent current from flowing between the gate electrode 101 and the semiconductor source region 103, drain region 105 or channel region 109.
In operation, an output voltage is typically developed between the source and drain terminals. When an input voltage is applied to the gate electrode 101, a transverse electric field is set up in the channel region 109. By varying the transverse electric field, it is possible to modulate the conductance of the channel region 109 between the source region 103 and drain region 105. In this manner an electric field controls the current flow through the channel region 109. This type of device is commonly referred to as a MOS field-effect-transistors (MOSFET).
Semiconductor devices, like the one described above, are used in large numbers to construct most modern electronic devices. In order to increase the capability of such electronic devices, it is necessary to integrate even larger numbers of such devices into a single silicon wafer. As the semiconductor devices are scaled down (i.e., made smaller) in order to form a larger number of devices on a given surface area, the structure of the devices and fabrication techniques used to make such devices must be altered.
One important step in the manufacture of MOS devices is the formation of the gate electrode and the gate insulating layer. Typically, this is done by first growing a layer of silicon dioxide (usually 30 to 40 angstroms thick) over the substrate. Next, a polysilicon layer is deposited over the silicon dioxide layer and etched to form a gate electrode. Etching of the polysilicon layer is typically performed using well-known photolithography and etching techniques. This conventional technique for forming the gate electrode and gate insulating layers however imposes limitations on the processing of the semiconductor device. For example, spacers must be provided on the resultant electrode structure prior to silicidation of the gate electrode and adjacent active regions in order to prevent shorting the gate electrode to the active regions. As a result, alternative techniques for forming the gate electrode and gate insulating layer are needed.